Pump control system

ABSTRACT

A pump control system characterized in that the pressure drop across a variable area orifice embodied in a directional control valve for a fluid motor is utilized to vary the displacement of the pump so that the fluid motor is actuated at desired speed irrespective of variation of pump speed and motor load. The system is further characterized in that it embodies a power limiting device which senses increasing motor load pressure to decrease the displacement of the pump as the horsepower requirement approaches the maximum available horsepower. Yet a further characterizing feature of the present system is the provision of a pump de-stroking valve which is disposed in the pump output circuit upstream of the directional control valve to provide a bypass to the reservoir to maintain standby power drain at a low value.

v o United tates Patent [1 1 [111 3,726,@93

Malott Apr. 10, 1973 PUNIP CONTROL SYSTEM Primary ExaminerEdgar W. Geoghegan [75] Inventor: Thomas J. Malott, Mentor, Ohio Attorney wa1ter Maky [73] Assignee: Parker-Hannifin Corporation, [57] ABSTRACT Cleveland, Ohio A pump control system charactenzed in that the pres- Flledi 1971 sure drop across a variable area orifice embodied in a [21] Appl. No.1 198,747 directionalcontrol valve for a fluid motor is utilized to vary the displacement of the pump so that the flllld motor is actuated at desired speed irrespective of [52] U-S. Cl ..60/445 variation of pump speed and motor load The ystem [51] Int. Cl. ..FlSb 15/18, FlSb 15/22 i f h h t i d in that it embodies a power Fleld Of Search VS, IIE, device enses increasing motor load 60/52 R pressure to decrease the displacement of the pump as the horsepower requirement approaches the maximum References Cited available horsepower. Yet a further characterizing fea- NTS ture of the present system is the provision of a pump UNITED STATES FATE de-stroking valve which is disposed in the pump out- R25,702 12/1964 De Biasi ..60/52 VS put circuit upstream of the directional control valve to 2,941,365 6/1960 Ca lson e VS provide a bypass to the reservoir to maintain standby BUH'OUghS power drain at a low value 3,465,5 l9 9/1969 McAlvay et al. ..60/52 VS 11 Claims, 1 Drawing Figure 8 2o II /112's A 32 I9 6 38 I5 I7 s Is 23 a. lo

PATENTEB 3,726,093

l/fl p llv m in PUMP CONTROL SYSTEM BACKGROUND OF THE INVENTION It is known, as in the case of an axial piston pump, to provide a control piston which senses the pressure drop across a variable orifice in the pump and which engages the cam plate or wobble plate of the pump to maintain a pre-selected output flow regardless of pump speed and load. However, such pump when employed in a hydraulic system including a fluid motor and a spool type directional control valve entails high spool flow forces and high parasitic horsepower losses because such preselected output flow must pass through the directional control valve and metering of the flow through the directional control valve to the fluid motor is not possible except by bleed off of a portion of the pump output downstream of the variable orifice. It is also known to use overload relief valves in connection with such pumps to prevent over-loading but again resulting in power loss.

SUMMARY OF THE INVENTION Contrary to known variable volume pumps, the pump control system herein utilizes the variable area metering orifice of a directional control valve to vary the output flow of the pump, the control piston of the pump sensing the pressure drop across said variable area orifice to enable variation of the speed of actuation of the fluid motor controlled by the directional control valve in accordance with the setting of the variable area orifice.

The system herein also embodies motor load pressure limiting means which decreases the pump output flow when the demand set by the variable orifice and the motor load pressure approaches the maximum available horsepower.

When the directional control valve is of the closed center type the system also embodies a de-stroking valve which automatically bypasses the pump output to minimize standby power drain when the directional control valve is in neutral position closing the pump control variable orifice therein.

Other objects and advantages of the present invention will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWING The lone FIGURE is a cross-section view somewhat diagrammatic in character illustrating a hydraulic system embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION The hydraulic system herein comprises a variable volume pump 1 having therein a displacement adjusting mechanism 2 and a power limiting valve 3; a directional control valve 4; a fluid motor 5; a de-stroking valve 6; and an optional de-stroke valve 7 for remote de-stroking of the pump 1.

By way of illustrative example, the pump 1 herein is an axial piston pump, the housing 8 of which has an inlet port 9 communicating with a fluid reservoir 10 and anoutlet port 11 communicating by way of conduit 12 with the inlet port 14 of the directional control valve housing 15. The pump drive shaft 16 is journaled in the pump housing 8 and has splined thereto a cylinder block 17, said cylinder block 17 having a circular array of bores in which the pistons 18 reciprocate through strokes determined by the angular position of the cam plate or swash plate 19 which is tiltable about the axis of the support shaft 20 thereof. As well known, the cylinder block 17 and housing 8 have mating plane valve surfaces with the housing surface opening in kidney shaped inlet and outlet slots with which the cylinder openings 21 in the cylinder block surface successively register as the pistons 18 move upwardly and downwardly. The pistons 18 are biased by springs 23 in an upward direction and are connected at their upper ends to thrust plates 24 which bear against the inclined bottom face of the swash plate 19. The cylinder block 17 and housing 8 valve surfaces are urged into sealing engagement not only by the piston biasing springs 23, but also by the center springs 25 which urge the retainer plate 26 upwardly against the bottoms of the thrust plates 24. The swash plate 19 has a lever arm 27 which is coupled by means of pin 28 to the control piston 29 of the pump adjusting mechanism 2 and to the control rod 30 of the power limiting valve 3.

The directional control valve4 herein shown is of the four-way closed center type for controlling the actuation of the double acting fluid motor 5 and comprises the housing 15 having a bore intersected axially therealong by the inlet port 14, by a pair of motor ports 31 and by a pair of return ports 32. The motor ports 31 are communicated with the ports of the fluid motor 5 by way of check valves 34 one of which opens when the associated motor port 31 is pressurized and the other of which is cam-opened when the associated motor port 31 is communicated with the adjacent return port 32.

Reciprocable in the housing 15 is a cam spool 35 which, when in the neutral position asshown, has a land 36 which blocks communication of the inlet port 14 with both motor ports 31, the latter then being open to the respective return ports 32. The spool land 36 has variable area orifices or metering slots 37 therein to meter the flow of fluid under pressure from the inlet port 14 to a selected motor port 31, thus to control the speed of actuation of the fluid motor 5 in either direction. When the spool 35 is actuated to the right from the neutral position, fluid under pressure in the inlet port 14 flows through the left set of variable area orifices 37 into the left motor port 31 to open the left check valve 34 for flow of fluid into the head end of the motor 5 and when the spool is thus shifted to the right, the right cam 38 thereon opens the right check valve 34 for return flow of fluid from the rod end of the motor 5 into the right motor port 31 and into the right return port 32. When the spool 35 is shifted to the left from the neutral position, fluid under pressure flows from the inlet port 14 into the right motor port 31 via the right-hand set of variable area orifices 37 and flows through the check valve 34 into the rod end of the motor 5, and the left cam 38 unseats the left check valve 34 for return flow of fluid from the head end of the motor 5 into the left motor port 31 for flow into the left return port 32. The check valves 34 may be of the pilot operated type such as disclosed in the copending U. S. Pat. application of Hugh .1. Stacey, Ser. No. 7,836, filed Feb. 2, 1970 and in the patent to Hugh J. Stacey U.S. Pat. No. 3,216,448 granted Nov. 9, 1965.

As known, the flow Q through an orifice having a pressure drop A P, an area A, and an orifice coefficient K is established by the following formula:

Hence, if the adjustment mechanism 2 is responsive to departure from a constant AP, the flow Q through the orifices 37 is directly related to the area a A thereof i.e. the position of the spool 35 in the directional control valve housing 15. In the present case, the adjustment mechanism 2 decreases the output flow of the pump 1 when the pressure drop across the orifices 37 exceeds AP (for example 50 p.s.i.) and increases the output flow of the pump 1 when the pressure drop across the orifices 37 is less than AP. To accomplish this result, the control piston 29 has a lost-motion connection with the piston rod 43 of a sensing piston 45, the latter having opposite sides thereof exposed to fluid pressure upstream and downstream of the orifices 37 viz, the pressures in passage 42 and in the feedback conduit 40. When the pressure differential AP is 50 p.s.i., the spring 46 acting on the piston rod 43 maintains the latter in a position whereat the chamber 47 is vented to the low pressure inlet chamber 48 within the pump 1 via the passages 49.

The housing has two passages leading from the respective motor ports 31 to a feedback conduit 40 via the check valves 41 in the respective passages, said feedback conduit 40 passing through the de-stroke valve 7 which may be provided for remote de-stroking of the pump 1 and through the power limiting valve 3 to the pump displacement adjusting mechanism 2.

Also leading to the pump adjusting mechanism 2 is a passage 42 from the pump outlet 11 whereby said pump adjusting mechanism 2 has conducted thereto fluid pressures of different magnitudes upstream and downstream of the variable area orifices 37 whereby the pressure drop across such orifices 37 is utilized to actuate the pump adjusting mechanism 2 in a manner now to be described in detail.

If the pressure drop across the variable area orifice 37 at any setting of the spool 35 is less than AP i.e. 50 psi. thereby indicating a lower output flow than desired, the pressure differential (less than 50 p.s.i.) on opposite sides of the sensing piston 45 will permit the spring 46 to close the passages 49 whereby upstream pressure builds up in the chamber 47 through orifice 50 to urge the control piston 29 upwardly to increase the tilt angle of the swash plate 19 whereby the pump displacement will be increased to desired value to actuate the fluid motor 5 at desired speed. As the pressure drop AP increases to 50 psi. the upstream pressure on the top of the sensing piston 45 moves the same downwardly against the spring 46 to re-open the passages 48 thus to vent the chamber 47 and thereby discontinue the upward movement of the control piston 29.

On the other hand, if the spool 35 is moved to decrease the flow area of the variable area orifice 37 with accompanying higher pressure drop exceeding 50 p.s.i. across said orifice 37, the upstream pressure acting downwardly on the sensing piston 45 will, through the pin connection 51 between the control piston 29 and the piston rod 43, pull the control piston 29 downwardly whereby the swash plate 19 is positioned at a smaller tilt angle with resulting lower displacement of the pump 1 so as to match the setting of the variable area orifice 37.

5 justing mechanism 2 while the other check valve 41 is held closed.

The pump 1 has in the feedback circuit a power limiting valve 3 which vents the feedback downstream thereof and closes the feedback upstream thereof when the load pressure in the feedback conduit 40 and in the pressurized motor port 31 increases to a value in relation to the pump 1 output flow nearing the available horsepower input to the pump 1. As evident, the horsepower input to the pump 1 varies as the product of the output flow and the load pressure and hence the power limiting valve 3 herein is designed to limit the load pressure in reverse relation to the output flow to avoid overloading of the pump 1. This is accomplished by providing a limiting valve member 54 which is held in the position shown by the limiter spring 56 whereby load pressure in the feedback conduit 40 is conducted to act on the lower side of the sensing piston 45 either to maintain an output flow as set by the position of spool 35 or to vary the output flow as commanded by movement of the spool 35 to increase or decrease the area of the variable area orifice 37.

When the product of the commanded output flow and the load pressure approaches the maximum available horsepower input to the pump 1, the load pressure in the feedback conduit 40, acting on the area A of the limiting valve member 54 will move it upwardly against the bias of the limiter spring 56 to close the feedback conduit 40 upstream of the valve member 54 and to vent the feedback conduit 40 downstream of the valve member 54 whereby the sensing piston 45 will move downwardly to decrease the output flow and to compress the limiter spring 56 to re-open the limiting valve 3. As aforesaid, horsepower varies as the product of the output flow and load pressure and when the swash plate 19 is at a low displacement position, a higher load pressure may be tolerated whereby the limiter spring 56 is compressed to greater degree at such low displacement position than at a higher displacement position of the swash plate 19. Accordingly, the limiter spring 56 force is inversely proportional to the displacement of the pump 1 so that overloading of the pump 1 cannot occur.

In the feedback circuit there is an optional destroke valve 7 for remote de-stroking of the pump 1. When the valve member 57 is moved downwardly the upstream portion of the feedback conduit 40 is blocked and the downstream portion of the feedback conduit 40 is opened to the reservoir 10, thus to decrease the pressure on the underside of the sensing piston 45 whereby the control piston 29 will be moved downwardly to a minimum displacement position.

The de-stroking valve 6 comprises a valve housing 58 having ports 59 and 60 respectively connected to the pump output conduit 12 and to the reservoir 10 and a port 61 connected to the feedback conduit 40 whereby the valve member 62 is exposed to the differential pressures upstream and downstream of the variable orifice 37 when the spool 35 is in operating position. However, when the spool 35 is shifted to neutral position, the pressure in the feedback conduit 40 decreases to tank pressure whereupon the inlet pressure in conduit 12 acting on the valve member 62 urges the same toward the left against the bias of spring 63 thus to open communication between the inlet line 12 and the reservoir through the fixed bypass orifice 64 in the valve member 62. The bias spring 63 on the de-stroke valve member 62 is designed to require, for example, a 25 percent increase in pressure above the normal control differential pressure of say, 50 psi. to overcome its load. Once the inlet line 12 pressure meets this pressure requirement, the de-stroke valve member 62 shifts to the left to uncover the fixed bypass orifice 64 to the reservoir 10. The orifice 64 area is selected such that only a small output flow from the pump 1 is needed to maintain enough pressure drop across the de-stroke orifice 64 to keep the de-stroke valve member in shifted position. Because the de-stroke pressure drop is also the pump control differential, the pump 1 is commanded to a minimum stroke at a low working pressure.

In summary therefore, it can be seen that the present hydraulic system provides a pump 1 output flow which in the case of rectangular metering orifices 37 as shown is linearly related to the spool 35 position. Moreover, the power demands on the system are matched to the load and are limited to the available horsepower whereby if the output flow demand setting is too great in relation to load pressure, the pump 1 is de-stroked to avoid overloading. Moreover, the de-stroking valve provides for a minimum standby power drain.

I, therefore, particularly point out and distinctly claim as my invention:

1. A fluid power system comprising a variable volume pump means, a directional control valve, and a fluid motor operatively interconnected whereby fluid delivered by said pump means is conducted to said fluid motor via said directional control valve; said directional control valve having variable area orifice means to determine the speed of actuation of said fluid motor; and said pump means having output adjustment means responding to the pressure drop between the upstream and downstream sides of said orifice means to adjust the output of said pump means according to the flow demand set by said variable orifice means.

2. The system of claim 1 wherein said directional control valve comprises a housing, and a valve member movable in said housing to vary the flow area of said orifice means.

3. The system of claim 1 wherein said directional control valve comprises a housing having a bore intersected axially therealong by an inlet port communicated with the outlet port of said pump means, a motor port communicated with said fluid motor, and a return port adapted for communication with a fluid reservoir; and a valve spool reciprocable in said bore from a neutral position whereat communication between said inlet and motor ports is blocked to operating positions selectively communicating said motor port with said inlet port via said orifice means or with said return port.

4. The system of claim 1 wherein feedback conduit means intercommunicates said directional control valve with said adjustment means to conduct fluid pressure on the downstream side of said orifice means to said adjustment means; and wherein said pump means has a passage communicating the pump output pressure upstream of said orifice means with said adjustment means whereby said adjustment means is exposed to both pressures for movement by the difference to a position increasing or decreasing the output flow of said pump according to the flow demand set by said orifice means.

5. The system of claim 1 wherein a power limiting valve isolates excessive load pressure downstream of said orifice means from said adjustment means and vents such downstream pressure from said pump adjustment means whereby the latter by reason of predominance of upstream pressure acting thereon adjusts said pump to a lower output flow to preclude overloading thereof.

6. The system of claim 5 wherein said power limiting valve is operatively coupled to said pump means to progressively decompress a spring means acting on said limiting valve thus to progressively decrease the maximum load pressure under increasing output flow conditions of said pump means.

7. The system of claim 1 wherein said directional control valve is of the closed-center type in which a valve member therein has neutral and operating positions which respectively block or permit flow of fluid from said pump means to said fluid motor; and wherein a de-stroke valve is operatively interposed between said pump means and said directional control valve to open restricted communication between the upstream side of said orifice means and a fluid reservoir when said valve member is in neutral position and to close such restricted communication when said valve member is in operating position; said de-stroke valve having a destroke valve member therein exposed to pressure upstream and downstream of said orifice means and movable under predominant fluid pressure on the upstream side of said orifice means to open restricted communication as aforesaid, the predominant upstream pressure being effective to actuate said adjustment means to adjust said pump means to a minimum displacement position when said directional control valve member is in neutral position.

8. A fluid power system comprising a variable volume pump means, a directional control valve, and a fluid motor operatively interconnected whereby fluid delivered by said pump means is conducted to said fluid motor via said directional control valve; said directional control valve comprising a housing, and a valve member movable in said housing and defining therewith a variable area orifice means to determine the speed of actuation of said fluid motor according to the position of said valve member in said housing; and said pump means having output adjustment means responsive to increase or decrease of pressure drop between the upstream and downstream sides of said orifice means above or below a predetermined value to decrease or increase the output of said pump means according to decrease or increase of the area of said orifice means as determined by the position of said valve member in said housing.

9. The system of claim 8 wherein said valve member comprises a valve spool reciprocable in a bore in said housing and wherein said orifice means comprises metering slots in said spool which vary in flow area according to the position of said spool in said housing.

10. The system of claim 8 wherein a feedback conduit means between said directional control valve and said pump adjustment means conducts fluid pressure downstream of said orifice means to act on one side of a piston in said pump adjustment means and wherein said pump means has a passage communicating with the output port of said pump means upstream of said orifice means to act on the other side of said piston, said pump adjustment means maintaining a constant output of said pump means upon predetermined pressure differential acting on opposite sides of said piston, said piston being interconnected to said pump means to increase or decrease the output of said pump means in response to decrease or increase of the pressure dif- 

1. A fluid power system comprising a variable volume pump means, a directional control valve, and a fluid motor operatively interconnected whereby fluid delivered by said pump means is conducted to said fluid motor via said directional control valve; said directional control valve having variable area orifice means to determine the speed of actuation of said fluid motor; and said pump means having output adjustment means responding to the pressure drop between the upstream and downstream sides of said orifice means to adjust the output of said pump means according to the flow demand set by said variable orifice means.
 2. The system of claim 1 wherein said directional control valve comprises a housing, and a valve member movable in said housing to vary the flow area of said orifice means.
 3. The system of claim 1 wherein said directional control valve comprises a housing having a bore intersected axially therealong by an inlet port communicated with the outlet port of said pump means, a motor port communicated with said fluid motor, and a return port adapted for communication with a fluid reservoir; and a valve spool reciprocable in said bore from a neutral position whereat communication between said inlet and motor ports is blocked to operating positions selectively communicating said motor port with said inlet port via said orifice means or with said return port.
 4. The system of claim 1 wherein feedback conduit means intercommunicates said directional control valve with said adjustment means to conduct fluid pressure on the downstream side of said orifice means to said adjustment means; and wherein said pump means has a passage communicating the pump output pressure upstream of said orifice means with said adjustment means whereby said adjustment means is exposed to both pressures for movement by the difference to a position increasing or decreasing the output flow of said pump according to the flow demand set by said orifice means.
 5. The system of claim 1 wherein a power limiting valve isolates excessive load pressure downstream of said orifice means from said adjustment means and vents such downstream pressure from said pump adjustment means whereby the latter by reason of predominance of upstream pressure acting thereon adjusts said pump to a lower output flow to preclude overloading thereof.
 6. The system of claim 5 wherein said power limiting valve is operatively coupled to said pump means to progressively decompress a spring means acting on said limiting valve thus to progressively decrease the maximum load pressure under increasing output flow conditions of said pump means.
 7. The system of claim 1 wherein said directional control valve is of the closed-center type in which a valve member therein has neutral and operating positions which respectively block or permit flow of fluid from said pump means to said fluid motor; and wherein a de-stroke valve is operatively interposed between said pump means and said directional control valve to open restricted communication between the upstream side of said orifice means and a fluid reservoir when said valve member is in neutral position and to close such restricted communication when said valve member is in operating position; said de-stroke valve having a de-stroke valve member therein exposed to pressure upstream and downstream of said orifice means and movable under predominant fluid pressure on the upstream side of said orifice means to open restricted communication as aforesaid, the predominant upstream pressure being effective to actuate said adjustment means to adjust said pump means to a minimum displacement position when said directional control valve member is in neutral position.
 8. A fluid power system comprising a variable volume pump means, a directional control valve, and a fluid motor operatively interconnected whereby fluid delivered by said pump means is conducted to said fluid motor via said directional control valve; said directional control valve comprising a housing, and a valve member movable in said housing and defining therewith a variable area orifice means to determine the speed of actuation of said fluid motor according to the position of said valve member in said housing; and said pump means having output adjustment means responsive to increase or decrease of pressure drop between the upstream and downstream sides of said orifice means above or below a predetermined value to decrease or increase the output of said pump means according to decrease or increase of the area of said orifice means as determined by the position of said valve member in said housing.
 9. The system of claim 8 wherein said valve member comprises a valve spool reciprocable in a bore in said housing and wherein said orifice means comprises metering slots in said spool which vary in flow area according to the position of said spool in said housing.
 10. The system of claim 8 wherein a feedback conduit means between said directional control valve and said pump adjustment means conducts fluid pressure downstream of said orifice means to act on one side of a piston in said pump adjustment means and wherein said pump means has a passage communicating with the output port of said pump means upstream of said orifice means to act on the other side of said piston, said pump adjustment means maintaining a constant output of said pump means upon predetermined pressure differential acting on opposite sides of said piston, said piston being interconnected to said pump means to increase or decrease the output of said pump means in response to decrease or increase of the pressure differential acting on opposite sides of said piston.
 11. The system of claim 10 wherein said feedback conduit means has therein a power limiting valve which isolates excessive load pressure downstream of said orifice means from said pump adjustment means and vents such downstream pressure from said pump adjustment means whereby the latter by reason of increase in pressure differential acting on opposite sides of said piston adjusts said pump means to a lower output flow to preclude overloading thereof. 